1. Field of the Invention
The present invention relates to a cathode-ray tube display device which displays images using a cathode-ray tube.
2. Description of the Prior Art
FIG. 1 is an exploded perspective view of a principal portion of a conventional cathode-ray tube display device disclosed, for example, in Swiss Patent No. 309701. In the same figure, the reference numeral 1 denotes a cathode-ray tube (hereinafter referred to as "CRT"); the numeral 2 denotes a deflecting coil unit mounted to a neck portion of the CRT 1; numeral 3 denotes a circuit board mounted to the deflecting coil unit; numeral 4 denotes a lead wire drawn out from the circuit board 3; numeral 5 denotes a connector connected to the lead wire; numeral 6 denotes a metallic reinforcing band for explosion-proof wound round a panel portion 1a of the CRT 1; numeral 7 denotes a cabinet which houses therein substantially the whole of the device; and numeral 8 denotes a front cover which encloses therein the panel portion 1a of the CRT 1.
Referring to FIG. 2, which is a side view of the CRT 1, the numeral 1b denotes a funnel portion body other than the panel portion 1a, the panel portion body 1b being divided into a funnel portion 1c, a cone portion 1d and a neck portion 1e. Numeral 9 denotes an electron gun disposed in the interior of the neck portion 1e; numeral 11 denotes an anode button provided in the funnel portion 1c; and numeral 12 denotes a resistance material, e.g. graphite, applied to the funnel portion 1c for imparting capacitance to the CRT 1. The panel portion 1a and the funnel portion 1c are sealed and bonded together using fritted glass, and the reinforcing band 6 is wound round a boundary portion between the two.
In FIG. 3, which is a perspective view of the deflecting coil unit 2, the numeral 13 denotes a coil mounting body constituted by a trumpet-shaped insulator; numeral 14 denotes a vertical deflecting coil mounted on the outer peripheral surface of the coil mounting body 13; and numeral 15 denotes a horizontal deflecting coil mounted on the inner peripheral surface of the coil mounting body 13. The deflecting coil unit 2 of such a construction is mounted on the neck portion 1e of the CRT 1, as shown in FIG. 1, and a front end portion thereof is in contact with the cone portion 1d.
FIGS. 4 and 5 are a perspective view and a sectional side view, respectively, showing a horizontal width adjusting coil unit, in which the numeral 16 denotes a horizontal width adjusting coil unit; numeral 17 denotes a coil bobbin; numeral 18 denotes a coil wound round the coil bobbin 17; and numeral 19 denotes a screw core for inductance adjustment which is movable vertically in the interior of the coil 18. The horizontal width adjusting coil unit 16 of such a construction is used in connection with a fly-back transformer (not shown).
The operation of such conventional cathode-ray tube display device will be described below.
A vertical deflecting current and a horizontal deflecting current are fed to the vertical deflecting coil 14 and the horizontal deflecting coil 15 of the deflecting coil unit 2, and a video signal is fed to the electron gun 9, whereby an electron beam from the electron gun 9 is deflected. This electron beam is radiated to a phosphor of R.G.B. applied to the surface of the panel portion 1a, whereby the panel surface is rendered luminous and an image is displayed thereon. By adjusting the screw core 19 of the horizontal width adjusting coil unit 16, the horizontal width of the screen is adjusted.
Since the conventional cathode-ray tube display device is constructed as above, an alternating electric current is generated from the coils and transformers of the deflecting coil unit 2 and the horizontal width adjusting coil unit 16 and sometimes the leakage thereof to the exterior affects the peripheral devices. Recently, a standard for restricting the generation of such alternating electric field has been established, so there arose the necessity of taking some measures to meet the standard. In this connection, there has been proposed a method in which a resistance material is provided on the tube surface and is connected to ground to shield electrostatically the alternating electric field leaking in the tube axis direction from the deflecting coil unit 2. However, a satisfactory effect has not been obtained yet.